Background: Bacterial lysates are known to modulate the immune response against respiratory infections. However, the effects of the commercial bacterial lysate Pulmonarom^® on dendritic cells—particularly human monocyte-derived dendritic cells (moDCs)—have not been studied. Additionally, limited data are available on the expression of Toll-like receptors (TLRs) and cytokines following stimulation with bacterial lysates. Methods: Human monocytes were isolated from buffy coats and differentiated into moDCs. Pulmonarom^® was lyophilized, quantified, and used to stimulate moDCs. Ultrastructural changes were evaluated using transmission electron microscopy. The expression of TLRs and selected cytokines was analyzed by flow cytometry. Results: Pulmonarom^® stimulation induced morphological changes in moDCs, including an increased number of dendrites and lysosomes. It also led to the upregulation of MHC class II molecules and TLRs 2, 3, 6, and 7. Additionally, the production of IL-4, IL-6, IL-8, and MCP-1 was significantly increased. Conclusions: Pulmonarom^® promotes moDC maturation, characterized by enhanced antigen presentation capabilities and lysosomal activity, along with increased expression of specific TLRs and cytokines. These features suggest a trained immunity phenotype in moDCs, potentially improving their ability to initiate adaptive immune responses against respiratory pathogens. To our knowledge, this is the first study to investigate the immunomodulatory effects of Pulmonarom^® on human moDCs, providing novel insights into its potential as an immunotherapeutic adjuvant.

Background Evidence shows bacterial lysates may participate in the immune response against respiratory infections. However, few studies have been conducted on dendritic cells, and, to our knowledge, none on human dendritic cells, and few have analyzed certain TLRs and cytokines. Materials and Methods Monocytes were obtained from the buffy coat and subsequently differentiated into dendritic cells (moDCs). The protein of commercial bacterial lysate Pulmonarom® was lyophilized and quantified. Ultrastructural changes induced by Pulmonarom® were evaluated in moDC by electron microscopy, and the expression of TLRs and some cytokines in these cells was evaluated by flow cytometry. Results Pulmonarom®-stimulated moDCs showed increased numbers of dendrites and the presence of lysosomes; they also showed increased expression of MHC-II and TLRs 2, 3, 6, and 7, IL-4, IL-6, IL-8, and MCP-1. Major conclusions The effects of Pulmonarom® on moDC correlate with an increased capacity to mobilize to lymph nodes and present antigens, initiating an effective adaptive immune response. Lysosomal activity and maturation of moDC, increased expression of TLR2, TLR3, TLR6, and TLR7 receptors, and increased production of the cytokines IL-8, MCP-1, IL-6, and IL-4, indicate a training process in moDC after their activation with Pulmonarom® bacterial lysate. This suggests that Pulmonarom® could enhance responses against viruses and bacteria by activating moDC. To our knowledge, this is the first study to address the effect of Pulmonarom® on one of the most important cells orchestrating the innate and acquired immune responses.